On Mon, Jan 15, 2024 at 11:23:59AM -0500, Steven Rostedt wrote:
> On Mon, 15 Jan 2024 11:09:38 -0500
> Steven Rostedt <rost...@goodmis.org> wrote:
>
> > No. The ring buffer logic should not care if the user of it is swapping
> > the entire ring buffer or not. It only cares if parts of the ring
> > buffer is being swapped or not. That's not the level of scope it should
> > care about. If we do not want a swap to happen in update_max_tr()
> > that's not ring_buffer.c's problem. The code to prevent that from
> > happening should be 100% in trace.c.
>
> What needs to be done, and feel free to add this as a separate patch,
> is to have checks where snapshot is used.
>
> (All errors return -EBUSY)
>
> Before allowing mapping, check to see if:
>
> 1) the current tracer has "use_max_tr" set.
> 2) any event has a "snapshot" trigger set
> 3) Any function has a "snapshot" command set
Could we sum-up this with a single check to allocate_snapshot? If that is
allocated it's probably because we'll be using it?
That would simply add the requirement to echo 0 > snapshot before starting the
memory map?
The opposite could be to let tracing_alloc_snapshot_instance() fail whenever a
mapping is in place?
>
> Fail if any of the above is true.
>
> Also in reverse, if the buffer is mapped, then fail:
>
> 1) a tracer being set that has "use_max_tr" set.
> 2) a "snapshot" command being set on a function
> 3) a "snapshot" trigger being set on an event.
>
> For the last two, we may be able to get away with just a below as well.
> Adding the tr->flags bit. We could also add a tr->snapshot count to
> keep track of everything that is using a snapshot, and if that count is
> non-zero, mapping fails.
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 2a7c6fd934e9..f534f74ae80f 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1175,6 +1175,12 @@ static void tracing_snapshot_instance_cond(struct
> trace_array *tr,
> return;
> }
>
> + if (tr->flags & TRACE_ARRAY_FL_MAPPED) {
> + trace_array_puts(tr, "*** BUFFER IS MEMORY MAPPED ***\n");
> + trace_array_puts(tr, "*** Can not use snapshot (sorry) ***\n");
> + return;
> + }
> +
> local_irq_save(flags);
> update_max_tr(tr, current, smp_processor_id(), cond_data);
> local_irq_restore(flags);
>
>
> -- Steve
>
> --
> To unsubscribe from this group and stop receiving emails from it, send an
> email to kernel-team+unsubscr...@android.com.
>
